Acl parser + unit tests

pgLabII.PgUtils/Acls/AclParser.cs

@@ -0,0 +1,113 @@
+using System.Text;
+
+namespace pgLabII.PgUtils;
+
+public class Acl(string grantee, string rights, string grantor)
+{
+    public string Grantee { get; } = grantee;
+    public string Rights { get; } = rights;
+    public string Grantor { get; } = grantor;
+}
+/// <summary>
+/// Parser for acl's. Acl's have a fairly simple structure grantee=right/grantor see also https://www.postgresql.org/docs/current/ddl-priv.html
+/// When the grantee is empty it is "PUBLIC" which you can see as a wildcard that matches everybody that can authenticate.
+/// Because the grantee and grantor name can contain special characters there is an escape mechinism in place.
+/// When the name contains a conflicting character it is quoted. If the name contains a quote it is doubles. 
+/// </summary>
+public class AclParser
+{
+    private int _position = 0;
+    private string _input = null!;
+    
+    public Acl Parse(string acl)
+    {
+        _input = acl;
+        _position = 0;
+        ConsumeWhitespace();
+        string grantee = ConsumeRoleName();
+        string rights = ConsumeRights();
+        if (Current() != '/')
+            throw new ArgumentException("Unexpected symbol in acl string");
+        _position++;
+        string grantor = ConsumeRoleName();
+        return new Acl(grantee, rights, grantor);
+    }
+
+    /// <summary>
+    /// There is a limited set of possible characters for the rights
+    /// </summary>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    private string ConsumeRights()
+    {
+        if (Current() != '=')
+            throw new ArgumentException("Unexpected symbol in acl string");
+        _position++;
+        int start = _position;
+        while (NotAtEnd() && Current() != '/')
+            _position++;
+        
+        return _input.Substring(start, _position - start);
+    }
+
+    // Whitespace should have been consumed
+    // There should be either a " in which case the name is quoted
+    // a = in which case there is no name ie PUBLIC
+    // all other cases it is an unquoted name
+    private string ConsumeRoleName() =>
+        _input[_position] switch
+        {
+            '=' => "",
+            '"' => ParseQuotedName(),
+            _ => ParseUnquotedName()
+        };
+
+    private string ParseQuotedName()
+    {
+        _position++; // consume opening quote
+        int start = _position;
+        StringBuilder sb = new();
+
+        while (true)
+        {
+            while (NotAtEnd() && Current() != '"')
+                _position++;
+
+            char peek = _position + 1 < _input.Length ? _input[_position + 1] : '\0';  
+            if (peek == '"')
+            {
+                _position++;
+                sb.Append(_input.AsSpan(start, _position - start));
+                _position++;
+                start = _position;
+            }
+            else
+            {
+                sb.Append(_input.AsSpan(start, _position - start));
+                _position++;
+                break;
+            }
+        }
+
+        return sb.ToString();
+    }
+
+    private string ParseUnquotedName()
+    {
+        int start = _position;
+        while (NotAtEnd() && Current() != '=')
+            _position++;
+        
+        return _input.Substring(start, _position - start);
+    }
+
+    private void ConsumeWhitespace()
+    {
+        while (NotAtEnd() && char.IsWhiteSpace(Current()))
+            ++_position;
+    }
+    
+    private bool NotAtEnd() => _position < _input.Length;
+    
+    private char Current() => _input[_position];
+}